m42 timing chain guide replacement ?

[Simon S]

One of the preventative maintenance procedures I’d like to do is replace tensioner and all (4) guide rails for the m42 timing chain.

At 136K miles – I feel the chain and sprockets themselves will be good for just under another 100K. (sprocket teeth appear very solid currently)

While I have yet to read about a specific story yet – I have heard rumor of decaying (rubber/plastic) chain guide rails disintegrating and leading to catastrophic engine failure. I also believe that proactively replacing guide rails will help chain/sprockets to live a longer life.

That said – my question regards the replacement procedure itself. I don’t want to disturb timing alignment. Chain and sprockets will be left in place.

When swapping the guides out/in, are there any measures that need to be taken to ensure proper timing alignment? Is alignment setting at risk when removing slack from chain? (tensioner/tensioner guide removed)

Is a cam position lock tool needed?

So far, I’ve generated a parts order list including: 4 chain guides, gasket sets for upper/lower timing case, front main seal, circlip for fastening w/ tentioner guide, tensioner, and tensioner gasket. Anything else to get ‘while-I’m-in-there’?

timin chain case and timing chain pages from realOEM for reference..

Thanks for any guidance or input.

[KenC]

It's the old ones that were stamped steel with plastic lining that were the issue.

Also, you'll need to remove the gears and chain to replace the guides. And you guessed it, you'll need the cam lock tool.

[KenC]

How are your sprockets now?

Open it up and take a look at everything before you replace it. The parts are hella expensive.

Also, use RTV instead of the gaskets.

You'll need a new profile gasket set.

[MrSalumi]

Hey Simon,

I just got done doing this procedure along with many others. It's pretty simple. I replaced my chain as well since it was already out and it was only 56 bucks. The funny thing is that I almost decided not to take the lower timing cover off and complete this fix. Good thing I did because my lower guide rail was broken in two pieces, and the static (drivers side) rail has a massive bend in it. Frankly I'm surprised it ran.

I did it all without a cam locking tool. Just lock the flywheel at TDC through the bell housing with an allen wrench. Good luck!

[Simon S]

you'll need to remove the gears and chain to replace the guides.

Crap – you’re totally right. Looks like tensioner guide (left) and top guide could be swapped without disturbing the chain. The long guide at right, however, ‘wraps’ behind the chain – so yeah – chain would have to come out in order to replace it.


^ m42 build picture posted by peerless

A home-made cam locking tool might do the trick.


^ posted by BUDNUNTA

How are your sprockets now?
Open it up and take a look at everything before you replace it. The parts are hella expensive.

The valve cover was removed last Fall. Teeth on upper sprockets appeared to be in great shape. No detectable wear.

Yeah – it’s not like any one part is expensive – just that there are so many and it adds up fast.

It's the old ones that were stamped steel with plastic lining that were the issue.

Ug – no fair. Will have to dismantle whole front of engine and get timing cases off to inspect. (no idea what kind or what condition the guides are in)

So – if/when I do go to replace guides, I’m thinking to find TDC – then lock crank (via flywheel access hole from block), and lock cams in place via cam-locking tool. Once crank and cams are locked in place – proceed to remove sprockets/chain – then swap in new guides and put things back together. (?)


I may be over-thinking preventative maintenance here.. I’m wanting to replace things like fan clutch, water pump, and front crank seal – and thought replacing guides would be smart ‘while I’m in there’.

.. lower guide rail was broken in two pieces, and the static (drivers side) rail has a massive bend in it..

Oh snap – now I’m totally swapping new guides in! Thanks for jumping in. Good to know this is a ‘doable’ proceedure. How many miles were on the motor?

[KenC]

I did it all without a cam locking tool. Just lock the flywheel at TDC through the bell housing with an allen wrench. Good luck!

That doesn't make any sense. Locking the flywheel at TDC locks the crank, but doesn't do anything for the cams, which as soon as you remove the tension from the chain will rotate slightly due to pressure on the lobes. At TDC, the valves don't have much to move, and my guess is that the cam rotated slightly allowing the valves to rest on the pistons in cylinders one and four.

[KenC]

So – if/when I do go to replace guides, I’m thinking to find TDC – then lock crank (via flywheel access hole from block), and lock cams in place via cam-locking tool. Once crank and cams are locked in place – proceed to remove sprockets/chain – then swap in new guides and put things back together. (?)




- Yes. Set the crank at TDC, and then lock the cams in place before you remove anything. Inspect all the guides thoroughly, and replace any that need it.


It's a good time to replace your water pump too.

Don't even bother with that clutch fan. Pop in a lower temp switch and just let your aux fan cool the radiator. The only time my temp gauge even approached 3/4 mark was on 100F+ days with the A/C on and going uphill.

[z31maniac]

I guess I'm a "while you're in there" type of person.

I can't imagine pulling the sprockets/chain/guides, to just replace one guide rail. If I was going to do all that I'd just go ahead and replace everything. But I absolutely HATE doing the same labor twice on something, YMMV.

[txleadfoot]

I wouldn't worry too much about the chain guides unless you're hearing some noise. You should definitely check the torque on the upper oil pan bolts inside and out. Having done a few M42 overhauls, I can say that this "preventative" maintenance is probably uncalled for unless you have some ca$h to burn and/or have real concern.

[MrSalumi]

That doesn't make any sense. Locking the flywheel at TDC locks the crank, but doesn't do anything for the cams, which as soon as you remove the tension from the chain will rotate slightly due to pressure on the lobes. At TDC, the valves don't have much to move, and my guess is that the cam rotated slightly allowing the valves to rest on the pistons in cylinders one and four.

I know it doesnt do anything for the cams. In my scenarios I had the cams totally out and was putting everything back together. With the cams out and no pressure on the valves, I locked the crank at TDC and positioned the cams at TDC. Then tightened all the cam towers. I'm saying the Cam Lock tool wasnt necessary for me to align and set the cams. However I do like the homemade locking tool! Good one on that.

[Simon S]

Thanks guys - really appreciate the input.

[blalor]

Just wanted to say thanks for the info and pics posted in this thread. The previous owner of my 318is replaced the timing chain tensioner(s?), but I'm hearing a lot of what I believe to be chain noise. I'm gearing up to do the work and saw the required "special tools" in the Bentley manual; I found exactly was looking for here: an alternative to those tools!

[blalor]

I did it all without a cam locking tool. Just lock the flywheel at TDC through the bell housing with an allen wrench. Good luck!

Typing this from my garage at the moment. :) Where is the hole in the bell housing? The picture in the Bentley E36 manual may as well be of a piece of my anatomy.

[Simon S]

Typing this from my garage at the moment. :) Where is the hole in the bell housing? The picture in the Bentley E36 manual may as well be of a piece of my anatomy.

One way to put it would be: "below the starter".

Here's a picture of the white plug to remove for said hole. You can see shift arm carrier in the transmission tunnel behind it.

[blalor]

Thanks, Simon. That's the first I've heard/seen of that plug. It's missing on mine.